Can't identify where this lip is in hiding in this model
Probably not (yet) an answer, but at least I can show something that seems weird in your model:





You have some different faces for interior and exterior sides of your bag, but their normals are all directed outwards, instead of being as usual, ie: I expected the exterior face normal pointing outside, and the interior face normal pointing inside the bag.

It seems there are many face normals set like this, it seems a bit weird imho.

I will try to learn Threejs basic concepts to experiment (never used before, but interesting) but I would try before making this mesh look better in Blender before...

edit: imho, this mesh has many problems (many of them clearly found by the 3d print addon mesh checker, or the mesh analysis tool, btw) which can confuse an external engine: face distortion (non planar) face overlaps, and others...